It has been around for a while now, but Apple – as with a lot of other technology – is the first to offer it to the consumers, and not to enterprises alone. You can – for example – get Data Tiering in “BeyondRaid” data storage solutions, like Drobo.
So what’s the diff?
With Data Tiering, the data is never in more than one location – it’s fundamentally different from caching that way. If you loose the cache, no big deal, but if you loose a tier, you’re in trouble. (All the more reason to keep Time Machine running, ey?)
This is both a Pro and a Con; data-caching does not get you higher capacity, only higher speed, data-Tiering gets you both, but data-Tiering does not give you a fallback in case the high-speed tier drops out. Data-caching does.
Now then, what do we do with it, and why do we care?
Well, we want speed. Incredible speed. Waiting 2 minutes for an App to start is so 1999. We want it fast and we want it 20 seconds ago! But we also want more and more, we can’t live with “just” 128 or 256 GB of storage, we desperately need those terabytes.
We could get a Seagate Momentus XT Solid State Hybrid drive (damn, what a name); that would give you 750GB of storage with 8GB of SSD cache. Total storage is 750GB.
For desktop computers (not Apple at the moment) there is the Intel Smart Response Technology which gives us the same effect in separate components; 1 HDD + 1 SSD + the correct main board and we’re done. But combining the 1 TB with a 64 GB (supposedly the maximum size) still gets you 1 TB of storage. Nothing more, nothing less.
Microsoft ReadyBoost provides similar technology by utilizing an USB flash drive as a cache.
(read on, only one more page of ranting :P)